CD40 ligand (CD154) and tumour necrosis factor-related apoptosis inducing ligand (APO-2L) in haematological malignancies

The immune system contains a few B and T lymphocytes that are specific for a certain antigen. Because these cells are not capable of eliminating an invading pathogen, the immune system has developed a mechanism whereby upon encountering an invading pathogen, the few antigen-specific lymphocytes rapidly proliferate to generate a large number of B and T lymphocytes that are able to kill and eliminate the offending pathogen. During this antigen-driven lymphoproliferative process, the activated lymphocytes receive survival signals to allow them to live long enough to complete their job. After eliminating the offending pathogen, survival signals are downregulated and the immune response is downsized to maintain a stable lymphocyte number. When this tightly controlled mechanism is impaired, lymphoproliferative disorders may occur (Younes, 1999). Many members of the tumour necrosis factor (TNF) family are involved in this process. This review will focus on two members of this family: TNF-related apoptosis inducing ligand (TRAIL, Apo-2L) and CD40 ligand (CD40L, CD154), and particularly their status in haematological malignancies.